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Open Ridge On Slate Roof


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I just did an inspection on a house in the old section of Pittsburgh. The house had a slate roof that has been pretty well maintained. The disclosure state that several of the shingles had been replaced in february .

My inspection showed little deterioration of the edges of the shingles and only one missing shingle. I inspected the roof from the roofs edge.

The inspection of the attic showed that the ridge shingles did not meet. they stay about 1/2 inches away from each other and there is no overlap ( open to the blue sky above) Someone had tried to seal the top with tar. (There were heavy tar inside on the planking.) I have not done that many inspection on slate roofs and I have Never heard of the ridge being open.

Can anyone give me any idea if this is an appropriate installation or if this is not proper. I need to figure out how to address this issue.



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I guess I don't have to tell you that seeing daylight is not a good thing. And the added insult of patching a ridge with roofing mastic on a slate roof is in my opinion, sacrilegious.

Roofing mastic is considered a temporary fix at best, I advise my clients to monitor those areas or make the appropriate repairs to avoid leakage.

Does the gap you are referring to, run along the entire ridge?

Does the roof have venting, as in roof vents, gable vents or turbines etc.?

If the roof doesn't have venting, other than eaves, it may be a misguided attempt at doing a ridge vent.

Regardless, the gap at the ridge is incorrect on any roofing material and needs to get fixed.

Along with the recommendation I would include the provision of vents if required, just to cover yourself.


Careful on recommending fixes, you could own the results and consequences.

A side note: Do you have a photo?

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Hi Aaron,

I'll echo Rob's sentiments. There should not be a gap there and I'm guessing that whatever was there has fallen away or been removed.

The ridge of most slate roofs is usually flashed with a lead or copper coping or covered with a saddle cap (or saddle ridge) of combing slates to cover that gap. Was the gap wide enough to have once held a vertical ridge backing block for a metal combing or did you happen to notice whether the top corners had been trimmed off the last course of roofing at either side of the ridge to allow installation of a saddle ridge?



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In the eastern part of the state, a majority of the older slate roofs do not have any ridge cap or cresting and saddled ridges are even more rare. Most slate roofs here have a "comb ridge" which the combing slates on the north or east side are laid to extend 1\4" to 1" over the other side. There is often a narrow gap that allows daylight to enter, but very little rain, unless wind driven. The frequency of water entry usually only produces some staining, but little damage, compared to a perpetual leak further down the collection surface of a roof. I have seen non professional repairs with roof cement to this type of gap, some even applied from the interior!

If the gap is significant, then I would lean towards Mike's opinion that something is missing.

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My experience mirrors Bill's. Ridge caps are great and I always recommend that they be installed where missing, but in Greater Boston, I'd guess that at least 1/3 of the slate roofs I see don't have them. Even after 100 years of exposed ridges in an area where we get about 46 inches of precipitation annually, I rarely find any associated damage.

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